Animal's weary, by the sound of it (4)
I believe the answer is:
boar
'animal's' is the definition.
(I've seen this before)
'weary by the sound of it' is the wordplay.
'weary' becomes 'bore' (as a verb).
'by the sound of it' indicates a 'sounds like' (homophone) clue.
'bore' sounds like 'BOAR'.
(Other definitions for boar that I've seen before include "Resting place for birds or bats" , "Male swine" , "Wild pig sounds tedious" , "A male pig, sounds tedious" , "The head for drink Falstaff had" .)